Litter production and nutrient resorption in western red cedar and western hemlock forests on northern Vancouver Island, British Columbia

Abstract

Fine litter fall and concentrations of N and P in green foliage and foliar litter were measured in three species over 1 year in two forest types at three sites on northern Vancouver Island to explore the hypothesis that differences in nutrient use and cycling between the dominant tree species on each forest type contribute to differences in forest floor nutrient availability. Total annual aboveground fine litter fall was significantly higher in second-growth, windstorm-derived 85-year-old stands of western hemlock (Tsugaheterophylla (Raf.) Sarg.) and amabilis fir (Abiesamabilis (Dougl.) Forbes) forests (4137 kg•ha−1) than in adjacent old-growth forests of western red cedar (Thujaplicata Donn) and western hemlock (3094 kg•ha−1) occurring on similar sites. Cedar had significantly lower N concentration in green foliage (9.3 mg•g−1) and litter (4.3 mg•g−1) than the other species in each forest type. Hemlock had a higher litter N concentration in the hemlock–amabilis fir type (8.3 mg•g−1) than in the cedar–hemlock type (6.4 mg•g−1). Cedar resorbed a significantly higher percentage of N during leaf senescence (76%), than hemlock in the cedar–hemlock type (64%), hemlock in the hemlock–amabilis fir type (51%), or amabilis fir (18%). Nitrogen-use efficiency (litter-fall mass/litter N) was considerably higher in cedar (235 kg litter/kg N) than in the other species in either forest type (90–156 kg litter/kg N). These results suggest that differences within and between species in the two types in nutrient use and the amount of nutrients cycling through the litter fall and internal redistribution pathways are contributing to lower rates of nutrient cycling and forest floor nutrient availability in the cedar–hemlock type.